linux-kernel - Re: [PATCH 5.10 21/63] kernel/io_uring: cancel io

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Date:   Mon, 4 Jan 2021 16:06:39 +0000
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Cc:     stable@...r.kernel.org, Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH 5.10 21/63] kernel/io_uring: cancel io_uring before task
 works

On 04/01/2021 15:57, Greg Kroah-Hartman wrote:
> From: Pavel Begunkov <asml.silence@...il.com>
> 
> commit b1b6b5a30dce872f500dc43f067cba8e7f86fc7d upstream.
> 
> For cancelling io_uring requests it needs either to be able to run
> currently enqueued task_works or having it shut down by that moment.
> Otherwise io_uring_cancel_files() may be waiting for requests that won't
> ever complete.

Greg, can you drop it from stable for now? I'll backport it later when
related problems are sorted.

> 
> Go with the first way and do cancellations before setting PF_EXITING and
> so before putting the task_work infrastructure into a transition state
> where task_work_run() would better not be called.
> 
> Cc: stable@...r.kernel.org # 5.5+
> Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
> Signed-off-by: Jens Axboe <axboe@...nel.dk>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> 
> ---
>  fs/file.c     |    2 --
>  kernel/exit.c |    2 ++
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> --- a/fs/file.c
> +++ b/fs/file.c
> @@ -21,7 +21,6 @@
>  #include <linux/rcupdate.h>
>  #include <linux/close_range.h>
>  #include <net/sock.h>
> -#include <linux/io_uring.h>
>  
>  unsigned int sysctl_nr_open __read_mostly = 1024*1024;
>  unsigned int sysctl_nr_open_min = BITS_PER_LONG;
> @@ -453,7 +452,6 @@ void exit_files(struct task_struct *tsk)
>  	struct files_struct * files = tsk->files;
>  
>  	if (files) {
> -		io_uring_files_cancel(files);
>  		task_lock(tsk);
>  		tsk->files = NULL;
>  		task_unlock(tsk);
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -63,6 +63,7 @@
>  #include <linux/random.h>
>  #include <linux/rcuwait.h>
>  #include <linux/compat.h>
> +#include <linux/io_uring.h>
>  
>  #include <linux/uaccess.h>
>  #include <asm/unistd.h>
> @@ -762,6 +763,7 @@ void __noreturn do_exit(long code)
>  		schedule();
>  	}
>  
> +	io_uring_files_cancel(tsk->files);
>  	exit_signals(tsk);  /* sets PF_EXITING */
>  
>  	/* sync mm's RSS info before statistics gathering */
> 
> 

-- 
Pavel Begunkov